In recent years, researches are being conducted on a body area network (BAN) in which communications are performed among a plurality of communication devices attached on different positions of a human body. BAN is expected to be used in, for example, health care applications. For example, wireless communications are conducted between a small communication device connected to a biological sensor attached to a certain portion of a human body such as, for example, a wrist and a controller attached to a different portion of the human body such as, for example, a torso thereby transmitting biological information obtained by the biological sensor to the controller. Then, the controller may transmit the biological information to, for example, a medical information management system installed in a medical institution through a wireless communication channel, together with identification information of a person who wears the controller or with controller's identification information.
As described above, in BAN, a communication device is attached to a human body. Accordingly, it is preferable that an antenna included in the communication device is small in size, and particularly preferable that the antenna has a smaller size in a direction perpendicular to a human body surface. Furthermore, in BAN, there may be cases where three or more communication devices are attached to a human body. In such cases, the communication devices each use a different frequency band. Accordingly, it is preferable that antennas included in communication devices used in BAN may be usable in a plurality of frequency bands.
On the other hand, patch antennas that are small in size and usable in a plurality of frequency bands are being proposed (for example, see Japanese Laid-open Patent Publications Nos. 2007-68096, 1994-303028, 2002-305409, 2003-258540 and Japanese National Publication of International Patent Application No. 2009-501467). The patch antennas disclosed in these patent documents each include a plurality of layered conductor plates (patches), and have better radiation characteristics in a direction perpendicular to surfaces of the conductors so as to make it usable in a global positioning system (GPS), for example.